1. Field of the Invention
The present invention relates to photographic printing apparatus. In particular, the present invention is an improved masking apparatus used in a photographic printer to create even width borders on bordered prints.
2. Description of the Prior Art
Photographic printers produce color or black-and-white prints from photographic film originals (generally negatives). High intensity light is passed through the film and imaged on the photosensitive print medium (generally photosensitive print paper). The photographic emulsion layers of the print paper are exposed and subsequently processed to produce a print of a scene contained in the film original.
Photographic prints are produced in a variety of different formats. One typical type of format used today is the "bordered" print in which a white border surrounds the printed image of the photographic print. This border is typically produced by a paper mask which is positioned between the photographic print paper and the optics of the printer which image light from the film original onto the paper. Bordered prints are produced by the use of a paper mask which defines an area of the print paper to be exposed to light which is smaller than the total area of the finished print. In this way, an unexposed border is produced around the exposed portion of the print paper. When developed, the unexposed portions of the print paper remain white, while the exposed portions of the print paper are darker or have a different color, depending upon the light to which they were exposed.
In typical photographic printers used in commercial photoprocessing operations, the unexposed photographic print paper is supplied from a supply roll, travels across a paper deck, and is wound onto a takeup roll. The paper mask is typically in close-spaced relationship to the paper deck, and the print paper advances through the space between the mask and the paper deck. The print paper is advanced across the paper deck and is stopped each time an exposure is made. In this manner, a large number of successive prints are made in edge-to-edge relationship on the strip of photographic print paper.
One difficulty which has been encountered with prior art photographic printers is that the widths and orientations of the white unexposed borders of bordered photographic prints vary in width and orientation. These variations arise from the fact that the paper mask in the prior art photographic printers is fixed in size and in position on the paper deck.
First, differences in width between the front and back borders occur if the centerline of the print paper is slightly misaligned with the centerline of the mask. In other words, the centerline of the paper strip is parallel to the centerline of the mask, but is shifted slightly toward either the front or the back. If the centerline of the paper is shifted toward the front with respect to the centerline of the mask, the front border is wider and the back border is narrower. Conversely, if the centerline of the paper is shifted to the back with respect to the centerline of the mask, the front border is narrower and the back border is wider. The paper misalignment typically occurs due to slight shifting of either the supply or takeup roll of photographic paper with respect to the centerline of the paper mask.
Second, variation in the width of the front and back borders can occur due to wander of the paper throughout feeding of the paper across the paper deck. In this case, the widths of the front and back borders of prints from the same roll of paper will vary.
Third, in some cases, the print paper can slightly angular mistrack across the deck. In other words, the centerline of the paper is skewed with respect to the centerline of the paper mask. In this case, the exposed area remains rectangular, but is skewed with respect to the edges of the print. All four borders of a skewed print are of differing width.
Fourth, variations in width of the print paper due to cutting tolerances and dimensional changes caused by humidity or other environmental conditions also cause variation in border widths of bordered prints. Since the mask is fixed with respect to the paper deck, the wider the print paper, the wider the front and back borders.
Uneven or skewed borders detract from the appearance of the photographic prints. This is a source of customer irritation or dissatisfaction.